This invention involves a dry, re-applicable adhesive apparatus.
Adhesives are widely used substances that ideally have a regulated amount of strength—adequate to the task and yet not so great that the adhesive itself cannot be broken or removed, or not so great that an adhered article cannot be moved and re-adhered. If an adhesive is to be used repeatedly, it should not have a strong (e.g., covalent) bond to the surface to which it adheres. This requirement removes an entire class of solutions. If the adhesive is to be a dry, non-liquid system, it is restricted to two types of known systems: (a) pressure-sensitive adhesives, or (b) interlocking type systems. Systems of type (a), pressure sensitive adhesives, fail because they rely upon very soft materials. These materials pick up dirt very easily, and are subject to long-term creep. The adhesion is also strongly dependent on rate of loading. Systems of type (b) require two mating surfaces and require the use of relatively large fibrils.
Many organisms have evolved a fibrillated interface for controlled contact and adhesion. As discussed in WO 01/49776, for example, the Gecko, appears to have evolved the ability to create dry, re-applicable adhesion to a variety of surfaces by relying only on weak van der Waals forces. Despite the low intrinsic energy of separating surfaces held together by van der Waals forces, these organisms are able to achieve remarkably strong adhesion. The microstructure employed by the Gecko, consisting of fibrils called setae and spatulae, plays a critical role in this ability.
Although the use of a fibrillar mat to mediate contact and adhesion is not limited to the example of the Gecko, quantitative relationships between parameters of a fibrillar structure and resulting contact and adhesion behavior have not been established. There remains a need to provide a synthetic fibrillar microstructure in which microstructural parameters are used to control contact and adhesion as the microstructure is applied against a surface and then pulled away.
It has been found that a fibrillar microstructure in which fibrils have a geometric properties such as length, width and aspect ratio, and have materials properties such as stiffness, adhesive energy and adhesive strength, as described herein, provides an apparatus having good conformal contact and adhesion at the interface thereof with a surface.